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  1. #1
    Join Date
    Feb 2010
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    779

    Default How fast does my prop spin?

    I have a 9 hp Volvo engine, single cylinder type, through a 110 saildrive. So how fast does my prop spin at max revs?

  2. #2
    Join Date
    May 2003
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    57,153

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    depends on the gear reduction
    engine what 3600 RPM 2 > 1 reduction
    I may be wrong but not always

  3. #3
    Join Date
    Jun 2001
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    3,504

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    I'd guess at slower than that. Avocet's got a single cylinder 1 horse BMW engine and a Hurth gearbox which has a 2.7 : 1 reduction going ahead. Probably doesn't rev much higher than about 3000 most of the time either.

  4. #4
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    May 2003
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    Quote Originally Posted by Avocet View Post
    I'd guess at slower than that. Avocet's got a single cylinder 1 horse BMW engine and a Hurth gearbox which has a 2.7 : 1 reduction going ahead. Probably doesn't rev much higher than about 3000 most of the time either.
    the OP stated WOT
    I may be wrong but not always

  5. #5
    Join Date
    Apr 2004
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    3200RPM at 1.66:1 => 1925RPM ???

  6. #6
    Join Date
    Nov 2007
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    19,078

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    Quote Originally Posted by PabloPicasso View Post
    I have a 9 hp Volvo engine, single cylinder type, through a 110 saildrive. So how fast does my prop spin at max revs?
    Your gearbox reduction ratio is 2.19:1. If your engine is a 2001 then max revs is 3200. So shaft speed is 3200/2.19 = 1461 rpm. Most Volvo saildrive combinations aim to get a shaft speed of around 1500 - for example the later 2010 has a reduction of 2.48 and a maximum revs of 3600 giving a shaft speed of 1451 - virtually the same as yours.

  7. #7
    Join Date
    Feb 2010
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    779

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    I'm just trying to assess how much oversized anodes on the hub of my folding prop might cause an imbalance problem. Current anodes can be done in 3 months. I'm looking for a solution and bigger anodes seems to be the most obvious one

  8. #8
    nimbusgb is offline Registered User
    Location : A long way from my boat! :(
    Join Date
    Oct 2005
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    Quote Originally Posted by PabloPicasso View Post
    I'm just trying to assess how much oversized anodes on the hub of my folding prop might cause an imbalance problem. Current anodes can be done in 3 months. I'm looking for a solution and bigger anodes seems to be the most obvious one
    3 Months! Find the electrical fault instead! Sounds like you have a serious leakage current! Is the boat connected to shore power a lot of the time?
    "Tomorrow to fresh woods and pastures new"

  9. #9
    macd is offline Registered User
    Location : Bricks & mortar: IoM. Me & boat: Turkey
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    Jan 2004
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    +1 with Nimbus.
    Prop anodes are concentric so won't cause imbalance. But that's not the way to go: fixing the leccy issue is what's needed. If on shore power, do you have a galvanic isolator?
    Mac

  10. #10
    Join Date
    Feb 2010
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    779

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    Quote Originally Posted by macd View Post
    +1 with Nimbus.
    Prop anodes are concentric so won't cause imbalance. But that's not the way to go: fixing the leccy issue is what's needed. If on shore power, do you have a galvanic isolator?
    No not never connected to shore power. On a swinging mooring. Battery disconnected by keys every time I leave the boat. This type of hub often seems to be reported as having anode problems like this. I believe, now, it is the quality of the hub itself and poor anode design. Hence the need to fit bigger anodes

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